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Visitors who braved the Willis Tower’s Skydeck got quite a surprise when they stepped out onto The Ledge. They thought it was cracking under them, 103 stories above the ground. Turns out it was just the protective coating, but they didn’t know that at the time. NBC 5’s Michelle Relerford spoke with them about their hair-raising experience. (Published Thursday, May 29, 2014)

Updated at 6:19 AM CST on Friday, May 30, 2014

All four boxes of The Ledge, the 103rd floor tourist attraction atop Chicago's Willis Tower, were closed Thursday morning for what an official said was a routine inspection.

The move comes hours after cracks appeared in what the official said was a coating designed to prevent scratches on the glass.

"Skydeck Chicago is open today while the protective coating is being replaced," said Brian Rehme, a spokesman for public relations firm FleishmanHillard. "We have temporarily closed the four Ledge boxes for routine inspection we hope to reopen them shortly."

Take a Peek Over "The Ledge"

"This coating does not affect the structural integrity of The Ledge in any way. Occasionally, the coating will crack, as it is designed to in order to protect the surface of the glass," Rehme said in a statement.

Still, it was a frightening experience for the family members visiting from California. Garibay said he and others were joking with staff about the strength of the boxes even before his group walked out into one of the boxes.

"They jokingly and confidently responded, 'It's unbreakable,' so we just went on," said Garibay.

While he and his family members were on the Ledge, Garibay said he heard cracking. They stepped off and alerted staffers.

"I walked them over so they could see and they were totally shocked and asked us to step away and then proceeded to start calling staff and techs and I don't know who else. When we pulled our phones to start recording and take pictures they asked us to leave right away," he said.

When the tourist experience opened in 2009, engineers said the boxes were composed of three layers of glass each about one half-inch thick. They were built to hold five tons, officials said.